It was business as usual in Detroit's Greektown entertainment district Thursday, hours after an underground cable failure catapulted a heavy iron manhole cover 10 stories to the top of the Atheneum hotel.

A little after 9 p.m., a loud boom could be heard echoing throughout Greektown. Two more soon followed. Smoke began to flow into the Atheneum and Fishbone's, the restaurant attached.

Hotel guests and restaurant patrons were asked to evacuate, said Deputy Detroit Fire Commissioner David Fornell, adding that his first call was about smoke on the eighth floor of the hotel.

Investigators worked late into the night, trying to assess the cause of the explosions. Since then, DTE Energy has come forward saying the incident was caused by an underground cable failure, which caused a manhole cover to burst from the ground.

At the Atheneum and Fishbone's, however, business is back to usual.

Fishbone's owner Nico Gatzaros was inside having breakfast with family members Thursday morning. He said the event was scary. He received a call from a manager as soon as the boom was heard and smoke began spilling into the restaurant, and he drove from his home in Grosse Pointe to the scene instantly.

"We were just happy nobody got hurt. That's a blessing. To be able to be open 12 hours later is great," said Gatzaros, who said the restaurant closed about two hours early Wednesday night. About 100 patrons were escorted out.

"People didn't know what it was at first," Gatzaros said, noting that manhole-cover explosions happen around Detroit "more frequently than people know."

DTE did not immediately respond to a request for information on how many manhole-cover explosions happen each year.

According to NBC News, which did a 2015 report on the trend, manhole-cover incidents are common, with New York City reigning as the king of the occasion. A 2014 report by Consolidated Edison noted that there were 3,369 manhole events in New York City that year, and of that number, 32 were explosions.

There is typically an increase in incidents in summer months, when air-conditioning use is at an all-time high.

“Cables get extremely hot because of (the) extra volume of electricity running through them because of air condition,” Allan Drury, the spokesman for Consolidated Edison told NBC News. “During the summer, we always encourage customers to use energy wisely.”

In terms of response time, Gatzaros noted that the Detroit Fire Department and Detroit Police Department were at the scene almost instantaneously.

Because the event involved an explosion, the Fire Department was leading the investigation and response.

"The situation was determined to involve fire, so the Fire Department primarily handled it, and we just assisted," said Detroit police spokesman Officer Dan Donakowski.

When asked whether the response would have been different had the incident happened on a busy weekend night or was caused by a more sinister source, such a terrorist attack, Donakowsi said that the police department has emergency procedures for various incidents.

"It just depends on the type of incident that took place."

Nancy Vicevic-Howard and Stephen Howard, from Ontario, had just arrived at the Atheneum when they heard the explosion. They were in the lobby of the hotel when a loud boom rattled the cavernous room.

The couple, like the rest of the hotel guests, were evacuated from the building and escorted off the street by police because of the fumes. They ended up going to a Greektown restaurant and drinking wine. They returned to their room about 1 a.m.

They said they spoke to another guest who had planned to go to bed at 9 p.m. and ended up closing down a bar because she didn't think she could return to the hotel.

"There was a bit of a smell when we walked in," said Howard, "But it went away."

When they walked out of the hotel Thursday morning, people were milling around the lobby.

"I immediately thought 'terrorists,' " said Howard. "But then I thought, this is Detroit; it's got a bad reputation for being a little dangerous. We've never been here before, so..."